...the paper provides a new theory, a new relativity theory. It remains to be seen whether this theory proposal (or at least the general idea of a second relativistic invariant) is realized in Nature.

Most citations are due to the fact that my paper raises a question which, a posteriori, appears to be rather natural to several colleagues: since we realized in 1905, in the celebrated Einstein Special-Relativity study, that Nature hosts a "relativistic invariant scale," the speed-of-light scale, it is then natural to wonder whether we might eventually discover a second such scale. Research in Quantum Gravity actually provides a very natural candidate for such a scale, the so-called "Planck energy scale" which should govern the magnitude of quantum-gravity effects.

  Does it describe a new discovery or new methodology that's useful to others?

In a sense my paper describes a new "discovery," but at this point it is only a discovery in theoretical physics: in arguing that we should wonder whether a second relativistic invariant exists, I also showed that the presence of such a second relativistic invariant can be accommodated in relativity with a rather small technical effort. So the paper provides a new theory, a new relativity theory. It remains to be seen whether this theory proposal—or at least the general idea of a second relativistic invariant—is realized in Nature. For that we need help from experiments. Some experiments that are relevant will start operation in a few years.

  How did you become involved in this research?

I was studying the possible relevance of quantum gravity for some reported observations of cosmic rays. In that context one possibility that myself and others were considering was a new relation between energy and the momentum of a particle (a relation which of course is identical to the one of special relativity at energies presently accessible, but would be different at very high energies). In thinking about these modified energy/momentum relations I came to realize that actually special relativity was discovered because the Michelson-Morley experiments provided evidence in support of a "new" energy/momentum relation (here "new" refers to the theories of the time: the special-relativity energy/momentum relation is different from the one of the previous relativistic theory, the one of Galilei). So it seemed natural for me to consider the possibility that history might be repeating itself, and once again the new energy/momentum relation could be a manifestation of a modification of the relativity transformations, requiring the introduction of a new relativistic invariant.

  Could you summarize the significance of your paper in layman's terms?

My paper proposes a new path toward a solution of the quantum-gravity problem—the problem of unifying gravity and quantum mechanics. This new path is based on a new relativity theory, which could itself deserve some interest.

Giovanni Amelino-Camelia
Dipartimento di Fisica
Univ. Roma "La Sapienza"
Roma, ITALY